Electrode structure, solid oxide cell, and method for manufacturing electrode structure

Abstract

This electrode structure includes: an electrode skeleton; first catalyst particles embedded in the electrode skeleton at certain portions and exposed from the electrode skeleton at other portions; and second catalyst particles formed from the same component as the first catalyst particles and bonded to the first catalyst particles.

Description

Electrode structure, solid oxide cell, and method for manufacturing electrode structure

[0001] The present invention relates to an electrode structure, a solid oxide cell, and a method for manufacturing an electrode structure.

[0002] As an electrode structure, a configuration in which catalyst particles are supported on an electrode skeleton is sometimes adopted. For example, in solid oxide cells such as solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs), a pair of electrodes is provided to sandwich an electrolyte layer. In such electrodes, a structure in which catalyst particles are supported on an electrode skeleton is sometimes used.

[0003] In relation to the above, Patent Document 1 (US 2018 / 0323443A) discloses forming an electrode layer from a porous ceramic, impregnating a first surface of the electrode layer with a catalyst precursor, forming a catalyst by heat treatment at 750 to 950°C, and again impregnating the first surface of the electrode layer with a catalyst precursor and forming a catalyst by heat treatment at 300 to 700°C.

[0004] Solid oxide cells are operated at high temperatures. However, continuous operation at high temperatures can cause sintering of catalyst particles supported on the electrode skeleton. When sintering occurs, the surface area of ​​the catalyst particles decreases, resulting in a decrease in the reaction efficiency at the electrode. In other words, the solid oxide cell deteriorates.

[0005] Therefore, an object of the present invention is to provide an electrode structure that can suppress sintering of catalyst particles.

[0006] In one aspect, the electrode structure according to the present invention comprises an electrode skeleton, first catalyst particles that are partially embedded in the electrode skeleton and partially exposed from the electrode skeleton, and second catalyst particles that are formed from the same components as the first catalyst particles and are bonded to the first catalyst particles.

[0007] In one aspect, the present invention relates to a solid oxide cell comprising a metal support, a planar electrode supported by the metal support, and an electrolyte layer formed on the electrode, the electrode having the electrode structure described above.

[0008] In one aspect, the present invention relates to a method for manufacturing an electrode, comprising the steps of: dissolving a first catalyst material, which is a precursor of first catalyst particles, with an electrode skeletal material to prepare a solid solution; preparing a slurry of the solid solution and forming the slurry into a sheet to form a green sheet; firing the green sheet in a reducing atmosphere to prepare a fired body at a temperature at which the first catalyst material is dissolves from the electrode skeletal material; impregnating the fired body with a solution containing a second catalyst material, which is a precursor of second catalyst particles, the second catalyst particles being formed from the same components as the first catalyst particles; and calcining the fired body after the impregnation step.

[0009] Fig. 1 is a schematic cross-sectional view showing a solid oxide cell according to an embodiment. Fig. 2 is a cross-sectional view showing a schematic structure of an electrode 3. Fig. 3 is a flowchart showing a method for manufacturing a solid oxide cell. Fig. 4 is a cross-sectional view showing a schematic method for manufacturing a solid oxide cell.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0011] (Outline) Fig. 1 is a schematic cross-sectional view showing a solid oxide cell 1 according to this embodiment. As shown in Fig. 1, the solid oxide cell 1 has a metal support 4 (a first metal support 4-1 and a second metal support 4-2), electrodes 3 (a first electrode 3-1 and a second electrode 3-2), and an electrolyte layer 2. These are stacked in the order of the first metal support 4-1, the first electrode 3-1, the electrolyte layer 2, the second electrode 3-2, and the second metal support 4-2.

[0012] One of the features of the solid oxide cell 1 according to this embodiment is the structure of the electrode 3. Fig. 2 is an enlarged view of Fig. 1, and is a cross-sectional view schematically showing the structure of the electrode 3 (first electrode 3-1 and / or second electrode 3-2). The electrode 3 includes an electrode skeleton 7, first catalyst particles 5-1, and second catalyst particles 5-2.

[0013] The electrode skeleton 7 is a part that becomes the skeleton of the electrode 3. The electrode skeleton 7 has a porous structure.

[0014] The first catalyst particles 5-1 are supported by the electrode skeleton 7. Parts of the first catalyst particles 5-1 are embedded in the electrode skeleton 7, and other parts are exposed from the electrode skeleton 7.

[0015] The second catalyst particles 5-2 are bonded to the first catalyst particles 5-1. Specifically, the second catalyst particles 5-2 are bonded to exposed portions of the first catalyst particles 5-1. The second catalyst particles 5-2 are formed from the same components as the first catalyst particles 5-1.

[0016] According to the above-described configuration, the first catalyst particles 5-1 are partially embedded in the electrode skeleton 7, and therefore the first catalyst particles 5-1 do not move. Because the first catalyst particles 5-1 do not move, the second catalyst particles 5-2 do not move either. This prevents aggregation of the catalyst particles. This prevents sintering during continuous operation at high temperatures.

[0017] The above-described configuration may be employed in at least one of the first electrode 3-1 and the second electrode 3-2. If the above-described configuration is employed in at least one of the first electrode 3-1 and the second electrode 3-2, sintering is suppressed in that electrode 3. However, the above-described configuration is preferably employed in both the first electrode 3-1 and the second electrode 3-2.

[0018] The above is an outline of this embodiment. Next, this embodiment will be described in detail.

[0019] (Solid Oxide Cell) In this embodiment, the term "solid oxide cell" is a general term for a solid oxide fuel cell (SOFC) and a solid oxide electrolysis cell (SOEC). In the following, a solid oxide fuel cell (SOFC) will be used as an example for explanation. However, this embodiment is not limited to a solid oxide fuel cell (SOFC) and can also be applied to a solid oxide electrolysis cell (SOEC).

[0020] The shape of the solid oxide cell 1 is not particularly limited, but is preferably a flat plate type. That is, the first metal support 4-1, the first electrode 3-1, the electrolyte layer 2, the second electrode 3-2, and the second metal support 4-2 are preferably all flat.

[0021] (Metal Supports) The first metal support 4-1 and the second metal support 4-2 are provided to support the first electrode 3-1 and the second electrode 3-2, respectively. By providing these metal supports 4, the overall shape of the solid oxide cell can be maintained even if each electrode 3 and the electrolyte layer 2 are thin.

[0022] The thickness of each metal support 4 is, for example, 50 to 1000 μm, preferably 100 to 500 μm.

[0023] The metal support 4 is porous. Because the metal support 4 is porous, it is possible to supply gases necessary for operation to the electrode 3 from the outside via the metal support 4.

[0024] The constituent material of the metal support 4 is not particularly limited, but preferably contains Fe and Cr. Preferably, the metal support 4 contains SUS.

[0025] (Electrodes) The electrodes 3 are the parts where electrochemical reactions occur during operation. One of the first electrode 3-1 and the second electrode 3-2 is an anode electrode, and the other is a cathode electrode.

[0026] The thickness of each electrode 3 is, for example, 0.3 to 50 μm, preferably 0.5 to 30 μm.

[0027] As described above, the electrode 3 (first electrode 3-1 and / or second electrode 3-2) has an electrode skeleton 7, first catalyst particles 5-1, and second catalyst particles 5-2.

[0028] (Electrode Skeleton) As described above, the electrode skeleton 7 has a porous structure. The electrode skeleton 7 is preferably made of ceramics. In the present invention, ceramics refers to a sintered body of an inorganic material, and is a concept that encompasses not only non-metallic oxides but also metal oxides. Preferably, the electrode skeleton 7 contains a solid oxide ceramic. As the solid oxide ceramic, zirconium oxide, cerium oxide, or the like can be used. In a more preferred embodiment, the electrode skeleton 7 contains zirconium oxide. The use of zirconium oxide can increase the strength of the electrode skeleton 7. Examples of zirconium oxide include stabilized zirconia doped with yttria, neodymium oxide, samarium, gadolinium, scandium, or the like.

[0029] (Catalyst Particles) The first catalyst particles 5-1 and the second catalyst particles 5-2 are substances that have the function of promoting the electrochemical reaction in the electrodes 3 during operation.

[0030] As described above, the first catalyst particles 5-1 and the second catalyst particles 5-2 are formed from the same component. Preferably, the first catalyst particles 5-1 and the second catalyst particles 5-2 are metal particles. More preferably, the first catalyst particles 5-1 and the second catalyst particles 5-2 contain at least one element selected from the group consisting of praseodymium, lanthanum, strontium, nickel, and cobalt. When the electrode 3 is an anode electrode, the first catalyst particles 5-1 and the second catalyst particles 5-2 preferably contain nickel. When the electrode 3 is a cathode electrode, the first catalyst particles 5-1 and the second catalyst particles 5-2 preferably contain at least one element selected from the group consisting of praseodymium, lanthanum, strontium, and cobalt.

[0031] As described above, the first catalyst particles 5-1 are partially embedded in the electrode skeleton 7, and other portions are exposed from the electrode skeleton 7. This structure can be confirmed by observing the electrode 3 using, for example, a TEM or an AFM. Specifically, the observation can be performed using a method such as that described in a non-patent document (Review on exsolution and its driving forces in perovskites, Ohhun Kwon et al., J. Phys. Energy 2 (2020) 032001).

[0032] The particle diameter of the first catalyst particles 5-1 and the second catalyst particles is, for example, 5 to 500 nm, and preferably 10 to 100 nm. These particle diameters can be confirmed by observing the electrode 3 with, for example, a TEM or an AFM.

[0033] (Electrolyte Layer) The electrolyte layer 2 is made of a solid oxide. Specifically, it is made of a dense solid oxide ceramic. The electrolyte layer 2 is only required to be capable of conducting oxide ions while being impermeable to gases. The solid oxide ceramic is not particularly limited, but an example thereof is zirconia oxide. The use of zirconia oxide makes it possible to realize an electrolyte layer 2 having high strength. Examples of zirconia oxide include stabilized zirconia doped with yttria, neodymium oxide, samarium, gadolinium, scandium, etc. The thickness of the electrolyte layer 2 is, for example, 0.5 to 20 μm, preferably 1 to 10 μm.

[0034] In a preferred embodiment, the electrode skeleton 7 contains zirconium oxide, and the electrolyte layer 2 also contains zirconium oxide. As will be described in detail later, during production, a laminate including the electrolyte layer 2 and the electrode 3 is sintered at high temperature. At this time, if both the electrode skeleton 7 and the electrolyte layer 2 contain zirconium oxide, interdiffusion of materials occurs between the electrolyte layer 2 and the electrode 3. As a result, the bonding strength between the electrolyte layer 2 and the electrode 3 can be increased.

[0035] (Manufacturing Method) Next, a method for manufacturing the solid oxide cell 1 will be described. Fig. 3 is a flowchart showing the method for manufacturing the solid oxide cell 1. Fig. 4 is a cross-sectional view schematically showing this manufacturing method, showing the configuration of the electrode 3 portion.

[0036] 3, the method for producing the solid oxide cell 1 according to this embodiment includes a step (S1) of preparing a solid solution of a first catalyst material and an electrode framework material, a step (S2) of producing a green sheet, a step (S3) of firing in a reducing atmosphere, a step (S4) of impregnating with a second catalyst material, and a step (S5) of calcining. Each step will be described in detail below.

[0037] (S1) Preparation of solid solution First, the first catalyst material and the electrode skeletal material are solid-solved. The first catalyst material and the electrode skeletal material are materials that serve as precursors of the first catalyst particles 5-1 and the electrode skeleton 7, respectively. For example, the first catalyst material and the electrode skeletal material are mixed in a solvent while being heated as necessary. This produces a mixed solution. The resulting mixed solution is then fired in an electric furnace or the like. This produces a solid solution of the first catalyst material and the electrode skeletal material.

[0038] For example, when the first catalyst particles 5-1 are metal particles, a metal salt or the like can be used as the first catalyst material, which is the precursor thereof. As the metal salt, for example, a nitrate or the like can be used. When the first catalyst particles 5-1 are praseodymium, Pr(NO ３ ) ３ ・6H ２ O and the like can be used.

[0039] The electrode skeleton material is not particularly limited. For example, when the electrode skeleton 7 is a stabilized zirconia doped with Y and Sc, the electrode skeleton material may be ZrOCl ２ ・8H ２ O, Y (NO ３ ) ３ ・6H ２ O and Sc(NO ３ ) ３ ・4H ２ A material containing O can be used.

[0040] The first catalyst material is used in an amount of, for example, 0.01 to 0.1 mole per mole of the electrode framework material.

[0041] The solvent used in preparing the mixed solution of the first catalyst material and the electrode skeletal material may be any solvent that dissolves the first catalyst material and the electrode skeletal material. For example, a solvent containing ethylene glycol, citric acid, and water may be used. The amount of solvent used may be any amount that dissolves the first catalyst material and the electrode skeletal material.

[0042] The firing temperature when firing the mixed solution is, for example, 1000° C. to 2000° C., preferably 1400 to 1600° C. The firing time is, for example, 1 to 10 hours.

[0043] (S2) Preparation of Green Sheet Next, the green sheet containing the solid solution is prepared as a green sheet for forming an electrode. For example, the solid solution is dispersed in a solvent to prepare a slurry. The slurry is then formed into a sheet by a tape casting method or the like. This results in a green sheet for forming an electrode. The slurry may contain a binder, a pore-forming agent, a dispersant, and the like, as necessary.

[0044] Similarly to the green sheets for forming electrodes, green sheets for forming metal supports and green sheets for forming electrolyte layers are also prepared. As with the green sheets for forming electrodes, these green sheets can also be produced by preparing a slurry containing precursor materials and using a tape casting method or the like.

[0045] Then, the green sheets for forming electrodes, the green sheets for forming metal supports, and the green sheets for forming electrolyte layers are laminated to obtain a green sheet laminate.

[0046] (S3) Firing (reducing atmosphere) Next, the green sheet laminate is fired in a reducing atmosphere to prepare a fired body. This results in a laminate including the metal support 4, the electrode 3, and the electrolyte layer 2. By firing in a reducing atmosphere, the ions (e.g., Pr) of the first catalyst material 6 that were present inside the electrode skeleton 7 of the electrode 3 are converted to ions (e.g., Pr ３＋) migrates toward the surface of the electrode skeleton 7. Specifically, oxygen defects are created on the surface of the electrode skeleton 7. Ions of the first catalyst material 6 that were present inside the electrode skeleton 7 migrate (diffuse) toward the oxygen defects. In other words, they migrate to the surface. Then, on the surface of the electrode skeleton 7, the ions of the first catalyst material 6 are reduced, agglomerate, and grow into nuclei. As a result, first catalyst particles 5-1 are formed on the surface of the electrode skeleton 7. Parts of the first catalyst particles 5-1 formed in this way are embedded in the electrode skeleton 7, and other parts are exposed from the electrode skeleton 7.

[0047] The fact that the first catalyst particles 5-1 partially embedded in the electrode skeleton 7 can be obtained by the above-described mechanism is understood to be, for example, an ex-solution method. For example, the above-described mechanism can be understood by referring to the description in the aforementioned non-patent document (The first observation of Ni nanoparticle exsolution from YSZ and its application for dry reforming of methane).

[0048] The calcination temperature and time in this step may be set to any conditions that allow the first catalyst material to be separated from the electrode skeleton material. For example, the calcination temperature is 1000 to 1500° C. The calcination time is, for example, 0.5 to 5 hours.

[0049] The environment in this step may be a reducing atmosphere, for example, an environment containing 5 to 10 vol % hydrogen and air.

[0050] (S4) Impregnation of Second Catalyst Material Next, a solution containing the second catalyst material is prepared. The second catalyst material is a substance that serves as a precursor for the second catalyst particles 5-2. The second catalyst material may be, for example, the same as the first catalyst material. The solvent may be, for example, pure water. The concentration of the second catalyst material is, for example, 0.01 to 1 (g / ml), preferably 0.08 to 0.2 (g / ml).

[0051] Subsequently, the prepared solution is impregnated into the electrode 3. For example, the solution is dripped onto the metal support 4. Since the metal support 4 has a porous structure, the slurry can be impregnated into the electrode 3 through the metal support 4.

[0052] (S5) Calcination Next, the laminate is calcined. At this time, since the second catalyst material contains the same elements as the first catalyst particles 5-1, it preferentially bonds to the first catalyst particles 5-1. In other words, the first catalyst particles 5-1 serve as a scaffolding for the formation of second catalyst particles 5-2 from the second catalyst material. As a result, as shown in FIG. 4, a configuration is obtained in which the second catalyst particles 5-2 are bonded to the exposed portions of the first catalyst particles 5-1.

[0053] Preferably, the above steps (S4) and (S5) are repeated multiple times (for example, four times), so that the electrode 3 contains a desired amount of second catalyst particles 5-2.

[0054] The calcination temperature in step (S5) is, for example, 500 to 1500°C, preferably 600 to 1000°C. The calcination time is, for example, 10 minutes to 3 hours. When steps (S4) to (S5) are performed multiple times, it is preferable to set the calcination temperature for the second and subsequent times lower than the initial calcination temperature. The initial calcination temperature is, for example, 700 to 1000°C. The second and subsequent calcination temperatures are, for example, 500 to 700°C.

[0055] The solid oxide cell 1 according to this embodiment can be obtained by the method described above.

[0056] (Operating Method) The solid oxide cell 1 according to this embodiment is operated at a high temperature (for example, 500°C or higher). For example, when the solid oxide cell 1 is an SOFC, a fuel gas is supplied to the anode electrode (one of the first electrode 3-1 and the second electrode 3-2), and an oxidant gas is supplied to the cathode electrode (the other of the first electrode 3-1 and the second electrode 3-2). At the anode electrode, an anode reaction (H ２ O+O ２ -→H ２ O + 2e － ) at the cathode electrode, the cathode reaction (O ２ +2e － →O ２－) progresses. This allows the power generation function to be realized. During operation, the electrode 3 becomes hot, which can cause sintering of catalyst particles. However, according to this embodiment, as described above, the catalyst particles do not move, so aggregation of particles is suppressed, and sintering is suppressed.

[0057] (Others) The above describes an embodiment of the present invention. In this embodiment, the solid oxide cell 1 is flat and has both a first metal support 4-1 and a second metal support 4-2. With this configuration, the solid oxide cell 1 is symmetrical in the stacking direction. As a result, the solid oxide cell 1 is less likely to warp, and flatness can be improved. However, this embodiment does not necessarily have to have both the first metal support 4-1 and the second metal support 4-2. For example, only the first metal support 4-1 may be provided, and the second metal support 4-2 may not be provided.

[0058] (Additional Notes) The following is a summary of the typical configuration and effects of this embodiment as an addition.

[0059] (Supplementary Note 1) An electrode structure having an electrode skeleton 7, first catalyst particles 5-1 that are partially embedded in the electrode skeleton 7 and partially exposed from the electrode skeleton 7, and second catalyst particles 5-2 that are formed from the same components as the first catalyst particles 5-1 and are bonded to the first catalyst particles 5-1.

[0060] According to this configuration, the movement of the first catalyst particles and the second catalyst particles is suppressed, and aggregation is prevented, thereby suppressing sintering.

[0061] (Supplementary Note 2) The electrode structure according to Supplementary Note 1, wherein the electrode skeleton contains zirconium oxide.

[0062] With this configuration, an electrode structure with high strength can be obtained.

[0063] (Supplementary Note 3) The electrode structure according to Supplementary Note 1 or 2, wherein the first catalyst particles and the second catalyst particles contain at least one selected from the group consisting of praseodymium, lanthanum, strontium, nickel, and cobalt.

[0064] With this configuration, the electrode reaction in the electrode structure can be promoted.

[0065] (Appendix 4) A solid oxide cell including a metal support 4, a planar electrode 3 supported by the metal support, and an electrolyte layer 2 formed on the electrode, wherein the electrode 3 has the electrode structure described in any one of Appendices 1 to 3.

[0066] With this configuration, a solid oxide cell in which sintering is suppressed is realized.

[0067] (Appendix 5) A solid oxide cell comprising: a first metal support 4-1; a planar first electrode 3-1 provided on the first metal support; an electrolyte layer 2 provided on the first electrode; a planar second electrode 3-2 provided on the electrolyte layer; and a second metal support 4-2 provided on the second electrode, wherein at least one of the first electrode 3-1 and the second electrode 3-2 has the electrode structure described in any one of Appendices 1 to 3.

[0068] With this configuration, the solid oxide cell has a symmetrical configuration in the stacking direction with the electrolyte layer 2 at the center, which results in a reduction in warpage of the entire cell.

[0069] (Supplementary Note 6) The solid oxide cell according to Supplementary Note 4 or 5, wherein the electrolyte layer contains zirconium oxide.

[0070] With this configuration, it is possible to obtain an electrolyte layer 2 having high strength.

[0071] (Supplementary Note 7) A method for manufacturing an electrode, comprising: a step (S1) of dissolving a first catalyst material, which is a precursor of first catalyst particles, with an electrode skeletal material to prepare a solid solution; a step (S2) of preparing a slurry of the solid solution and forming the slurry into a sheet to produce a green sheet; a step (S3) of firing the green sheet in a reducing atmosphere to prepare a fired body, the firing being performed at a temperature at which the first catalyst material is dissolves from the electrode skeletal material; a step (S4) of impregnating the fired body with a solution containing a second catalyst material, which is a precursor of second catalyst particles, the second catalyst particles being formed from the same components as the first catalyst particles; and a step (S5) of calcining the fired body after the impregnation step.

[0072] According to this method, it is possible to realize an electrode structure having the specific configuration described above.

Claims

1. An electrode structure comprising: an electrode skeleton; first catalyst particles that are partially embedded in the electrode skeleton and partially exposed from the electrode skeleton; and second catalyst particles that are formed from the same components as the first catalyst particles and are bonded to the first catalyst particles.

2. The electrode structure according to claim 1, wherein the electrode skeleton comprises zirconium oxide.

3. An electrode structure according to claim 1 or 2, wherein the first catalyst particles and the second catalyst particles contain at least one element selected from the group consisting of praseodymium, lanthanum, strontium, nickel, and cobalt.

4. A solid oxide cell comprising: a metal support; a planar electrode supported by the metal support; and an electrolyte layer formed on the electrode, wherein the electrode has the electrode structure described in claim 1.

5. A solid oxide cell comprising: a first metal support; a planar first electrode provided on said first metal support; an electrolyte layer provided on said first electrode; a planar second electrode provided on said electrolyte layer; and a second metal support provided on said second electrode, wherein at least one of said first electrode and said second electrode has the electrode structure described in claim 1.

6. A solid oxide cell according to claim 4, wherein the electrolyte layer contains zirconium oxide.

7. A method for manufacturing an electrode structure, comprising: a step of dissolving a first catalyst material, which is a precursor of first catalyst particles, with an electrode skeletal material to prepare a solid solution; a step of preparing a slurry containing the solid solution and forming the slurry into a sheet to produce a green sheet; a step of firing the green sheet in a reducing atmosphere to prepare a fired body, wherein the green sheet is fired at a temperature at which the first catalyst material dissolves from the electrode skeletal material; a step of impregnating the fired body with a solution containing a second catalyst material, which is a precursor of second catalyst particles, wherein the second catalyst particles are formed from the same components as the first catalyst particles; and a step of calcining the fired body after the impregnation step.

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